HILO, Hawai'i — Work continues on efforts to cover up contaminated soil on the site of the future Target and Safeway stores in Hilo, where high levels of arsenic, dioxins and petroleum compounds have been found.

"As far as I know, it's progressing," Department of Hawaiian Home Lands spokesman Lloyd Yonenaka said about efforts to prepare the East Maka'ala Street site for construction.

"We knew going in there were some remediations that need to be done," Yonenaka said. "They should be complete by the middle of May."

The contamination was uncovered in the mid-1990s in a study of the Hilo Wood Treating property north of the Target-Safeway site. That study found arsenic, chromium, copper and hexavalent chromium in the soil.

In July 2008, an investigation for former tenant Akana Petroleum found elevated levels of arsenic on the Target-Safeway site; the other heavy metals found at the wood treatment plant were not present.

DHHL then drew up a contract with the Target-Safeway partnership and agreed to reimburse the two companies for up to $1.5 million in rent credits to clean up the contamination.

The two stores brought in Tetra Tech EM, an international consulting firm with an office in Honolulu, to study the extent of the contamination on site and recommend a solution.

Tetra Tech collected soil samples in January 2009 and found elevated contamination of arsenic, dioxins and petroleum compounds.

Consultants from Tetra Tech did further studies on the site last summer, noting "significant amounts" of trash, abandoned vehicles, scrap metal and 55-gallon drums; eight of the drums had "a strong, chemical/solvent odor," according to a report from the firm.

The additional scrutiny found high levels of dioxins in at least one soil sample and bioaccessible arsenic concentrations of up to 310 parts per million.

Consultants recommended that Target and Safeway "cap" the site with at least a foot of uncontaminated fill dirt, estimating it would cost $150,000. Other methods, including removal of the contaminated soil and hauling it to the West Hawai'i Landfill or shipping off-island, were rejected as being less effective and more costly. They also recommended removal or recycling of all the solid waste items.

According to Tetra Tech, Keaukaha Community Association President Patrick Kahawaiolaa contacted the Department of Health to request that the contaminated soil be excavated and hauled off so the site could be used for residential purposes.

Kahana Albinio Jr., a property development agent for DHHL, responded that the site was intended solely for commercial or industrial purposes. No other comments were received during last December's public comment period.

The state Department of Health's Hazard and Emergency Response office approved the plan.

Officials from Tetra Tech EM did not respond to a request for comment.